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# In the x–y plane, what is the y–intercept of the line l?

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Intern
Joined: 18 Sep 2009
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In the x–y plane, what is the y–intercept of the line l? [#permalink]

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24 Sep 2009, 18:11
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In the x–y plane, what is the y–intercept of the line l?

(1) The slope of the line l is 3 times its y-intercept.
(2) The x–intercept of line l is –1/3

OPEN DISCUSSION OF THIS QUESTION IS HERE: in-the-x-y-plane-what-is-the-y-intercept-of-the-line-l-127702.html
[Reveal] Spoiler: OA

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Last edited by Bunuel on 29 Nov 2013, 09:44, edited 1 time in total.
Renamed the topic, edited the question and added the OA.

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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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25 Sep 2009, 02:51
3
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1) insuff.
l=> y=mx+n where m is slope and n is y intercept. so we can think it like.
y=3nx+n.
Therefore the y intercept, n, can be any value.
2)insuff.
it says, when y=0, x becomes -1/3. Thus in a line l=y=mx+n
0=-1/3m+n
3n=m
So it can be any value
it is same as 1.
Together
0=3n.-1/3+n
0=0
This does not give us anything. So insuff.
Lets plug in some numbers.
Say n=1
Then line becomes y=3x+1 both A and B works.
Say n=2 then line becomes y=6x+2 both A and B works

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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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29 Nov 2009, 13:43
I don't understand the explanation on this. OA is E) and I don't understand why...
When I take them together, I have y=0.

Can someone explain it (again) plzz

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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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29 Nov 2009, 15:41
Equation of a line is y = m*x + c
where m is the slope of the line and c is the y-intercept, the value of y when x is zero.

Stmt-1: m = 3 * c. We can deduce nothing about the value of c based on this information.
Stmt-2: x-intercept given is the value of x when y is zero. Therefore, 0 = m * (-1/3) + c.
Solving it, we again get m = 3 * c.

As you see, both statements are the same and there is no point considering them together for possibility of answer choice C coming right.

Hence, E.
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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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29 Nov 2009, 16:09
BarneyStinson wrote:
Equation of a line is y = m*x + c
where m is the slope of the line and c is the y-intercept, the value of y when x is zero.

Stmt-1: m = 3 * c. We can deduce nothing about the value of c based on this information.
Stmt-2: x-intercept given is the value of x when y is zero. Therefore, 0 = m * (-1/3) + c.
Solving it, we again get m = 3 * c.

As you see, both statements are the same and there is no point considering them together for possibility of answer choice C coming right.

Hence, E.

Thank you so much Barney! It is kind of clear now )
(5days left b4 my test )

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Re: In the xy-plane, what is the y-intercept of line? [#permalink]

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29 Nov 2013, 07:55
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Re: In the x–y plane, what is the y–intercept of the line l? [#permalink]

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29 Nov 2013, 09:45
Expert's post
1
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In the x–y plane, what is the y–intercept of the line l?

Equation of a line in point intercept form is $$y=mx+b$$, where: $$m$$ is the slope of the line; $$b$$ is the y-intercept of the line (the value of $$y$$ for $$x=0$$).

The question is $$b=?$$

(1) The slope of line l is 3 times its y-intercept --> $$m=3b$$. Not sufficient to calculate $$b$$.

(2) The x-intercept of line l is -1/3 --> x-intercept is the value of $$x$$ for $$y=0$$ --> $$0=-\frac{1}{3}m+b$$ --> $$m=3b$$. Same info as above. Not sufficient.

(1)+(2) Nothing new. Not sufficient.

For more on this issue please check Coordinate Geometry chapter of Math Book: math-coordinate-geometry-87652.html

OPEN DISCUSSION OF THIS QUESTION IS HERE: in-the-x-y-plane-what-is-the-y-intercept-of-the-line-l-127702.html
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Kudos [?]: 129078 [0], given: 12194

Re: In the x–y plane, what is the y–intercept of the line l?   [#permalink] 29 Nov 2013, 09:45
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